VPB 121: Veterinary Physiology - II (2+1)

RESPIRATION IN BIRDS

• The lungs are small and attached to ribs and are rigid; they do not expand or contract during the respiratory cycle. Large discrete air sacs are present. Both inspiration and expiration are active.
• Respiratory system beginning from external nares leads to nasal cavities, which open into pharynx. The air also passes through the mouth in to the respiratory system.
• Trachea begins with glottis and divides into two bronchi. At the division is the syrinx, which is the vocal organ in birds. The length and volume of the trachea is greater in birds than in mammals.
• Each lung contains one main intrapulmonary primary bronchus, which divides into these sets of secondary bronchi.
  • The Secondary bronchi divide into tertiary bronchi or parabronchi.
  • The three sets of secondary bronchi are
    • Mediodorsal
    • Medioventral
    • Lateroventral.
• The parabronchi connect the mediodorsal and medioventral secondary bronchi and also connect some secondary bronchi to the airsacs.
• Those parabronchi (structures that contain gas exchange tissues in their walls) that passes between mediodorsal and medioventral secondary bronchi are nearly parallel and are called as paleopulmonic parabronchi.
• Those that pass from mediodorsal and lateroventral secondary bronchi and intrapulmonic primary bronchus to the caudal airsacs are called neopulmonic parabronchi. Exchange of gases between lungs and blood occur in parabronchi.